This invention relates in general to dentistry, and more particularly to a device and a method for measuring the occlusal clearance when preparing a tooth for a cast restoration.
The occlusal clearance is the space created between two opposing teeth in preparing one or both of them for a cast restoration. Cast restorations are commonly known as caps, crowns and bridges. They involve replacing a portion of a tooth with an artificial replica which is secured to a remaining portion of the tooth or is secured to the adjacent teeth. To attach a cast restoration to a remaining portion of a tooth, there must be a minimum space between the remaining portion of the tooth and the opposing teeth when the two rows of teeth are at normal occlusion, that is, when the two rows of teeth are brought together in a closed position. Ordinarily, a dentist grinds down the remaining portion of the tooth to create this minimum space. An inadequate space can lead to a subsequent failure of the cast restoration. The minimum space (occlusal clearance) required for cast restorations is approximately 1 millimeter for metal restorations and 2 millimeters for porcelain to metal restorations.
An occlusal clearance indicator is a device used to measure the occlusal clearance. Present methods and devices for measuring the occlusal clearance are unreliable. In one method, the dentist, with the aid of a mouth mirror, has the patient bring the opposing rows of teeth together to normal occlusion and the dentist then attempts to make a subjective assessment of the clearance between the tooth receiving the restoration (tooth preparation) and the opposing tooth or teeth. The occlusal clearance, however, is obscured by the tongue, saliva, muscles of the cheeks and diminished light. It is difficult, if not impossible, to make accurate and visual assessments of the occlusal clearance intraorally.
Wax or other impression material is also used to measure occlusal clearance. The dentist places the wax over the tooth preparation and has the patient bite into it. The dentist then inspects the wax intraorally or removes it and emits light through it to estimate the wax thickness. This method does not result in reliable measurements. It is only an estimate of the occlusal clearance, not a direct measurement. Furthermore, the wax may stick to the teeth and distorts the impression when removing the wax, making the procedure even unsuitable for an estimate. Using impression materials can also be time-consuming. Many dentists use a material which must cool or set before it can be observed. Where multiple measurements are required, it is a particularly time consuming method for measuring occlusal clearance.
Recently, blotting paper has been used to measure occlusal clearance. This technique suffers many drawbacks. First, a three dimensional representation (a dental indentation) cannot be recorded on blotting paper. A dental indentation will enable the dentist to visually determine how much tooth structure is to be removed prior to completing sufficient occlusal reduction. Blotting paper is also awkward to handle. Customarily, two or more layers of blotting paper have to be cut into strips and held together by forceps. Sometimes marking paper is also wrapped around the blotting paper and must also be held by the forceps. These manipulations are time-consuming and undesirable.
It has been suggested to use rubber bands to measure occlusal clearance. If the rubber band pulls from between the teeth, then the space is wider than the rubber band. If the rubber band is held by the teeth, then there is insufficient space between the teeth. As with blotting paper, this method does not use standard dental material and a dental indentation cannot be recorded on it.
Finally, a calibrated ball gauge has been used to determine whether there is sufficient occlusal clearance for cast restoration. The gauge is essentially a probe having a ball on its end. The ball is slipped between the tooth preparation and the opposing tooth or teeth at normal occlusion to verify if there is sufficient occlusal clearance for a cast restoration. The ball may have a diameter calibrated to verify the desired clearance. As with the above methods, the ball gauge does not record an observable dental indentation. It is also not disposable and relatively expensive to manufacture.
The present invention overcomes the above limitations and has additional advantageous features.